Steel parts have heretofore been formed using cold forging or hot forging techniques which are well known in the art. In hot forging parts from steel, the material is initially heated to about 2000.degree. F. and higher. At these hot forging temperatures, substantial scale and decarburization of the steel occurs. Since the scale and decarburized surfaces must be removed to obtain the finished part, known hot forging techniques result in the waste of a certain amount of material; furthermore, such techniques are costly due to increased processing steps required to remove the scale and the higher energy consumption because of the high temperatures.
On the other hand, there are drawbacks to cold forming parts as well. Since the part is formed at or about room temperature, the reshaping or forming steps require substantially higher forces. This frequently necessitates a series of cold forming steps in which the material is formed into the desired part gradually. This increases die wear and noise associated with such processes. Furthermore, if the material is worked to a substantial degree over a series of forming stages, the strength of the part is increased and the part must therefore be annealed between successive cold forming operations to relieve internal stress, which adds to the time and cost of such processes.
To avoid the above drawbacks, warm forging may be utilized to form parts from materials at an intermediate temperature which is high enough to reduce the strength of the material and thereby facilitate forming, and yet is below the hot forging temperature at which scaling and decarburization occurs. One such warm forming method is disclosed in U.S. Pat. No. 3,557,587. Certain other patents disclose processes which include rolling and extruding steps carried out at "warm" temperatures so as to avoid the drawbacks of decarburization and scaling and/or to impart or improve desired metallurgical and mechanical properties to the steel. See U.S. Pat. Nos. 2,767,836; 2,767,837; 2,880,855; 3,076,361; 3,573,999, and "Warm Working of Steel", Gokyu, et al, translation of the Japanese Institute of Metal, 1968, Volume 9, Supplement, Pages 177-181.
Additionally, there are other known methods for bending or forging steel bars, rods or billets to form a desired product which methods include a warm forming or warm forging step. See U.S. Pat. Nos. 2,953,794; 3,720,087; 3,877,281; 4,312,210; 4,317,355; 4,608,851 and 4,805,437. No representation is made that any of the above cited references fairly represent the prior art or that such references are the most material references.
There has heretofore been lacking a method of making a high-strength steel part from a blank of steel possessing desired high-strength properties, which method includes a warm forming step whereby the blank is formed into a desired part and whereby the mechanical properties of the part remain substantially the same or greater than those originally possessed by the blank, and in which the part is produced without additional strengthening processing steps to impart mechanical strength properties to the steel part.